Biodegradable sheet, molded object obtained from the sheet, and process for producing the molded object

ABSTRACT

A biodegradable sheet that causes no environmental problems, has excellent heat resistance and impact resistance, and is capable of forming deep-drawn molded article and blister molded article having a complicated shape. The biodegradable sheet comprises a resin composition containing 75 to 25 mass % of a polylactic acid resin and 25 to 75 mass % of a polyester having a glass transition temperature of 0° C. or less and a melting point higher than the glass transition temperature of the polylactic acid resin based on total 100 mass %, and the polylactic acid resin in the sheet has a degree of crystallization of 45% or less. The method for producing a molded article from the biodegradable sheet includes the step of molding the biodegradable sheet at a temperature not lower than the melting point of the aliphatic polyester and lower than a temperature by 30° C. higher than the melting point of the polyester.

CROSS REFERENCE TO RELATED APPLICATION

This application is the U.S. national stage of International ApplicationNo. PCT/JP2003/008590, filed Jul. 7, 2003, which was published under PCTArticle 21(2) as Publication No. WO2004/005400 and of which the instantapplication claims the benefit, which in turn claims the benefit ofJapan Patent Application No. 2002-198829, filed Jul. 8, 2002. All theseapplications are incorporated herein by reference in their entirely.

TECHNICAL FIELD

The present invention relates to a biodegradable sheet, biodegradablemolded article, and a method for producing the molded article. Moreparticularly, the present invention relates to a biodegradable sheet andbiodegradable molded article having heat resistance and impactresistance, and a method for producing the molded article.

BACKGROUND ART

Polyethylene, polypropylene, polyvinyl chloride, polystyrene,polyethylene terephthalate and the like have been used as materials forfood containers such as cups and trays, blister packs, hot-fillcontainers and trays and carrier tapes for transporting electronicparts. The food containers and the like made of these plastic materialsare in many cases thrown away after one use. Therefore, there arises aproblem of their disposal after they are used and discarded. Resins suchas polyethylene, polypropylene, polystyrene and the like generate muchheat when they are burned, so that there is the fear that they willdamage the furnace during they are burned. Polyvinyl chloride generatesnoxious gases during burning. In addition, ordinary plastics are stablefor a long period of time in natural environment and has low bulkdensity, so that they will make landfill sites for reclamation of wastesshort-lived, break natural landscape or break environment in whichmarine organisms live.

Accordingly, research and development of materials that will be degradedand disappear with time under natural environment are being madeextensively. Biodegradable materials attract attention as suchmaterials. One of them is polylactic acid. Polylactic acid is graduallydisintegrated and decomposed in soil or water by hydrolysis orbiodegradation and finally gives rise to harmless decomposate by theaction of microorganisms. Further, polylactic acid generates a smallamount of heat when it is burned. Since the starting material is ofplant origin, it is advantageous in that one does not have to depend onpetroleum resources that is being exhausted.

However, polylactic acid has low heat resistance and therefore it is notsuitable as a material for containers that are used at high temperaturessuch as containers in which food to be heated are included or containersinto which hot water is poured. Further, containers made of polylacticacid are sometimes deformed or fused in the inside of a storehouse, orin the inside of a truck or ship during transportation since hightemperatures are reached there in summer seasons.

A technology of imparting polylactic acid with heat resistance includesa method of maintaining the temperature of a mold near a crystallizationtemperature of polylactic acid (80 to 130° C.) and highly crystallizepolylactic acid in the mold. This method requires a molding cycle thatis longer than ordinary and incurs high production costs since themolded article must be retained in the mold until the crystallization iscompleted. In addition, installation for heating the mold is necessary.On the other hand, it is known to impart polylactic acid with heatresistance by blending the polylactic acid with polyester. However, formof plastic products is diversified and blister packs having acomplicated shape or deep-bottomed molded article are needed;conventional polyester-blended polylactic acids are not materials thatare satisfactorily adapted for such shapes.

DISCLOSURE OF THE INVENTION

Therefore, in view of the above, it is an object of the presentinvention to provide a biodegradable sheet that is made of a materialcausing no environmental problems, has excellent heat resistance andexcellent impact resistance, and is capable of forming deep-drawn moldedarticle and blister molded article having a complicated shape. Anotherobject of the present invention is to provide a molded article from thebiodegradable sheet and a method for producing the molded article.

To achieve the above-mentioned objects, the biodegradable sheet of thepresent invention is composed of a resin composition containing apolylactic acid resin and a polyester, wherein the resin compositioncontaining 75 to 25 mass % of the polylactic acid resin and 25 to 75mass % of the polyester having a glass transition temperature of 0° C.or less and a melting point higher than the glass transition temperatureof the polylactic acid resin based on total 100 mass %, and wherein thepolylactic acid resin in the sheet has a degree of crystallization of45% or less.

According to another aspect of the present invention, the biodegradablesheet is composed of a resin composition containing a polylactic acidresin and a polyester, wherein the resin composition containing 75 to 25mass % of the polylactic acid resin and 25 to 75 mass % of the polyesterhaving a glass transition temperature of 0° C. or less and a meltingpoint of 90° C. or more based on total 100 mass %, and wherein thepolylactic acid resin in the sheet has a degree of crystallization of45% or less.

Here, the degree of crystallization of the polylactic acid resin may be20% or less.

Further, the polyester may be biodegradable aliphatic polyester otherthan the polylactic acid resin.

According to a still another aspect of the present invention, thebiodegradable sheet is composed of a resin composition containing apolylactic acid resin and a polyester, wherein the resin compositioncontaining 75 to 25 mass % of the polylactic acid resin and 25 to 75mass % of the polyester having a glass transition temperature of 0° C.or less and a melting point higher than the glass transition temperatureof the polylactic acid resin based on total 100 mass %, and wherein amolded article molded from the sheet has a volume reduction ratio of 6%or less.

The biodegradable sheet for deep-drawing of the present invention iscomposed of a resin composition containing a polylactic acid resin and apolyester, wherein the resin composition containing 75 to 25 mass % ofthe polylactic acid resin and 25 to 75 mass % of the polyester having aglass transition temperature of 0° C. or less and a melting point higherthan the glass transition temperature of the polylactic acid resin basedon total 100 mass %, and wherein the polylactic acid resin in the sheethas a degree of crystallization of 45% or less.

The molded article of the present invention comprises a sheet that iscomposed of a resin composition containing 75 to 25 mass % of thepolylactic acid resin and 25 to 75 mass % of the polyester having aglass transition temperature of 0° C. or less and a melting point higherthan the glass transition temperature of the polylactic acid resin basedon total 100 mass %, and having a volume reduction ratio of 6% or less.

Here, a biodegradable sheet in which the polylactic acid resin in thesheet has a degree of crystallization of 45% or less may be molded at amolded article temperature not lower than a melting point of thepolyester and lower than a temperature by 30° C. higher than the meltingpoint of the polyester.

According to another aspect of the present invention, the molded articleis molded from a biodegradable sheet that is composed of a resincomposition containing a polylactic acid resin and a polyester, whereinthe resin composition containing 75 to 25 mass % of the polylactic acidresin and 25 to 75 mass % of the polyester having a glass transitiontemperature of 0° C. or less and a melting point higher than the glasstransition temperature of the polylactic acid resin based on total 100mass %, and wherein the polylactic acid resin in the sheet has a degreeof crystallization of 45% or less, at a temperature not lower than amelting point of the polyester and lower than a temperature by 30° C.higher than the melting point of the polyester, and then postcrystallized at a temperature not lower than the glass transitiontemperature of the polylactic acid resin and lower than the meltingpoint of the polyester, and having a volume reduction ratio of 6% orless.

According to yet another aspect of the present invention, thebiodegradable sheet is used for the above-mentioned molded article.

The method for producing a molded article of the present inventioncomprises forming a molded article from a biodegradable sheet that iscomposed of a resin composition containing a polylactic acid resin and apolyester, wherein the resin composition containing 75 to 25 mass % ofthe polylactic acid resin and 25 to 75 mass % of the polyester having aglass transition temperature of 0° C. or less and a melting point higherthan the glass transition temperature of the polylactic acid resin basedon total 100 mass %, and wherein the polylactic acid resin in the sheethas a degree of crystallization of 45% or less, at a temperature notlower than a melting point of the polyester and lower than a temperatureby 30° C. higher than the melting point of the polyester.

Here, the molded article formed from the biodegradable sheet at themolding temperature may be post-crystallized at a temperature not lowerthan the glass transition temperature of the polylactic acid resin andlower than the melting point of the polyester.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described.

The biodegradable sheet of the present invention comprises a resincomposition that contains a polylactic acid resin and a polyester. Here,the polyester must have a glass transition temperature of 0° C. or lessand have a melting point higher than the glass transition temperature ofthe polylactic acid resin with which it is blended, and the polylacticacid resin in a formed sheet must have a degree of crystallization of45% or less. Further, the polylactic acid resin and polyester must beblended in amounts such that 75 to 25 mass % of the polylactic acidresin and 25 to 75 mass % of the polyester are blended, the sum of theresin and the polyester being 100 mass %. If the blending amount of thepolylactic acid resin is more than 75 mass %, heat resistance becomespoor and if the blending amount of the polylactic acid resin is lessthan 25 mass %, the resultant sheet and molded article have poorrigidity.

The polylactic acid resins used in the present invention includepoly(L-lactic acid) containing L-lactic acid as a structural unit,poly(D-lactic acid) containing D-lactic acid as a structural unit, acopolymer containing both L-lactic acid and D-lactic acid as structuralunits, i.e., poly(DL-lactic acid), and mixtures thereof.

In the present invention, to increase heat resistance and for otherpurposes, small amounts of non-aliphatic dicarboxylic acids such asterephthalic acid, non-aliphatic diols such as ethylene oxide adducts ofbisphenol A and so on may be used as copolymerizable components.Further, for the purpose of increasing the molecular weight, smallamounts of chain extenders, for example, diisocyanate compounds, epoxycompounds, acid anhydrides and so on may be used.

The polylactic acid resin used in the present invention may becopolymers with other hydroxycarboxylic acids such asα-hydroxycarboxylic acid units, or copolymers with aliphatic diolsand/or aliphatic dicarboxylic acids.

The other hydroxycarboxylic acid units that are copolymerized with thepolylactic acid resin include optical isomers of lactic acid (D-lacticacid for L-lactic acid, L-lactic acid for D-lactic acid), bifunctionalaliphatic hydroxycarboxylic acids such as glycolic acid,3-hydroxybutyric acid, 4-hydroxybutyric acid, 2-hydroxy-n-butyric acid,2-hydroxy-3,3-dimethylbutyric acid, 2′-hydroxy-3-methylbutyric acid,2-methyllactic acid, and 2-hydroxycarproic acid, and lactones such ascaprolactone, butyrolactone, and valerolactone.

The aliphatic diols that are copolymerized with the polylactic acidresin include ethylene glycol, 1,4-butanediol, and1,4-cyclohexyanedimethanol. Further, the aliphatic dicarboxylic acidsinclude succinic acid, adipic acid, suberic acid, sebacic acid, anddodecanedioic acid.

It is preferable that the polylactic acid resin has a weight averagemolecular weight in the range of 50,000 to 400,000, more preferably100,000 to 250,000. If the polylactic acid resin has a weight averagemolecular weight less than 50,000, practically acceptable physicalproperties are difficult to obtain and if the polylactic acid resin hasa weight average molecular weight of more than 400,000, the meltviscosity may become too high to give acceptable mold processability.

Polymerization methods that can be used for the polylactic acid resininclude known methods such as a condensation polymerization method, aring-opening polymerization method. For example, in the case ofcondensation polymerization method, direct dehydrocondensationpolymerization of L-lactic acid or D-lactic acid or a mixture of thesecan give rise to polylactic acid resins of any desired compositions.

Further, in the ring-opening polymerization method, a polylactic acidresin may be obtained by polymerizing a lactide, which is a dimer oflactic acid, using a catalyst selected as appropriate, for example, tinoctylate while using a polymerization adjusting agent as necessary.Lactides include L-lactide, which is a dimer of L-lactic acid,D-lactide, which is a dimer of D-lactic acid, and DL-lactide, whichconsists of L-lactic acid and D-lactic acid. These are mixed asnecessary and polymerized to obtain polylactic acid resins having anydesired compositions and degree of crystallizations.

In the present invention, it is necessary to blend the polylactic acidresin with a specified polyester in order to impart a sheet or moldedarticle thereof with heat resistance, impact resistance and moldingprocessability. The specified polyester has a glass transitiontemperature of 0° C. or less and a melting point higher than the glasstransition temperature of the polylactic acid resin with which thepolyester is blended. Generally, the glass transition temperature of thepolylactic acid resin is 50° C. to 60° C. For example, polyesters havinga melting point of 90° C. or more can exhibit the effect of the presentinvention. If the glass transition temperature of the polyester ishigher than 0° C., the effect of improving impact resistance isunsatisfactory. In consideration of impact resistance, it is preferablethat the polyester has a glass transition temperature of −20° C. orless. Further, if the melting point of the polyester is not higher thanthe glass transition temperature of the polylactic acid resin with whichthe polyester is blended, the resultant sheet and molded article mayhave unsatisfactory heat resistance.

In the present invention, it is preferable that a biodegradablealiphatic polyester other than the polylactic acid resin be used as apolyester. Examples of the biodegradable aliphatic polyester includepolyhydroxycarboxylic acids, aliphatic polyesters obtained bycondensation of an aliphatic diol and an aliphatic dicarboxylic acid,aliphatic aromatic polyesters obtained by condensation of an aliphaticdiol, an aliphatic dicarboxylic acid and an aromatic dicarboxylic acid,aliphatic polyesters obtained by ring-opening polymerization of a cycliclactone, synthetic aliphatic polyesters, aliphatic polyestersbiosynthesized in microbial cells, and so on.

The polyhydroxycarboxylic acids used herein include homopolymers andcopolymers of hydroxycarboxylic acids such as 3-hydroxy-butyric acid,4-hydroxy-butyric acid, 2-hydroxy-n-butyric acid,2-hydroxy-3,3-dimethylbutyric acid, 2-hydroxy-3-methylbutyric acid,2-methyllactic acid, and 2-hydroxycarpoic acid.

Examples of aliphatic diols that are used for aliphatic polyesters oraliphatic aromatic polyesters include ethylene glycol, 1,4-butanediol,1,4-cyclohexanediemthanol and so on. Further, examples of theabove-mentioned aliphatic dicarboxylic acid include succinic acid,adipic acid, suberic acid, sebacic acid, dodecanedioic acid and so on.Examples of the aromatic dicarboxylic acid include terephthalic acid,isophthalic acid and so on.

By selecting one or more compounds from each compound exemplified aboveas appropriate and performing condensation polymerization, aliphaticpolyesters or aliphatic aromatic polyesters can be obtained. Further,the molecular weight of the polyester may be increased by use ofisocyanate compounds as necessary to obtain desired polymers.

Aliphatic polyesters obtained by ring-opening polymerization of cycliclactones can be obtained by polymerization of one or more of cyclicmonomers such as ε-caprolactone, δ-valerolactone,β-methyl-δ-valerolactone.

Examples of the synthetic aliphatic polyester include copolymers of acyclic acid anhydride and an oxirane, for example, succinic acidanhydride and ethylene oxide, propylene oxide or the like.

Examples of the aliphatic polyester biosynthesized in microbial cellsinclude aliphatic polyesters biosynthesized by acetyl coenzyme A (acetylCoA) in microbial cells of microbes including Alcaligenes eutrophas. Thealiphatic polyesters biosynthesized in microbial cells is composedmainly of poly(β-hydroxybutyric acid (poly-3HB). However, in order toincrease practically useful characteristics as a plastic, it isindustrially advantageous to further copolymerize hydroxyvaleric acid(HV) to obtain a copolymer of poly(3HB-CO-3HV). Generally, it ispreferable that the copolymerization ratio of HV is 0 to 40 mol %.Further, in place of hydroxyvaleric acid, long chain hydroxyalkanoatessuch as 3-hydroxyhexanoate, 3-hydroxyocatanoate and3-hydroxyoctadecanoate may be copolymerized.

Examples of the biodegradable aliphatic polyesters that can be used inthe present invention include polybutylene succinate, polybutylenesuccinate adipate, polybutylene adipate terephthalate, polyglycolicacid, polyester carbonate, copolymers of polyhydroxybutyrate andpolyhydroxyvalerate, and copolymers of polyhydroxybutyrate andpolyhydroxyhexanoate. At least one selected from the group consisting ofthe above-mentioned polyesters is used.

Various modifications may be made to the resin composition of thepresent invention by addition of auxiliary additives. Examples of theauxiliary additive include heat stabilizers, light stabilizers,antioxidants, ultraviolet absorbents, pigments, colorants, antistaticagents, electroconducting agents, release agents, plasticizers,lubricants, inorganic fillers, fragrances, antimicrobials, nucleatingagents and the like.

In the present invention, a sheet can be tolerably formed from a resincomposition that contains a blend of a polylactic acid resin and aspecified in a predetermined proportion. However, the polylactic acidresin in the sheet must have a degree of crystallization of 45% or less,preferably 20% or less. The sheet in which the polylactic acid resin hasa degree of crystallization of more than 45% can be tolerably molded byvacuum forming, air pressure forming, vacuum-air pressure forming, andpress forming. However, when deep-drawn molded article having a drawratio (L/D: L is a depth of molded article, D is an aperture of moldedarticle) of 0.5 or more or a blister molded article having a complicatedshape is formed by vacuum forming, formability is poor and no goodmolded article can be obtained.

Generally used sheet forming method can be used as a method for formingthe sheet. For example, mention may be made of extrusion molding by aT-die cast method. However, since the polylactic acid resin is highlyhygroscopic and highly hydrolyzable, so that water control duringproduction process is necessary. For example, when extrusion molding isperformed using a monoaxial extruder, it is preferable that film formingbe performed after dehumidification and drying by a vacuum drier or thelike. On the other hand, when extrusion molding is performed using avent-type biaxial extruder, dehydration effect is high so that efficientfilm formation is possible. It is also possible to form a multilayersheet by using a plurality of extruders.

The biodegradable sheet of the present invention can be set to asuitable thickness depending on utility. When a molded article is formedby using the biodegradable sheet of the present invention, a sheethaving a thickness that corresponds to a thickness required to aresultant molded article is selected. For example, in the case of traysfor foods such as fresh fish, meat and so on, the thickness of the sheetis preferably 100 μm to 500 μm. Note that “sheet” means a product thatis thin and flat, and has a thickness that is small as compared with thelength and width as defined by JIS. On the other hand, “film means athin, flat product that has an extremely small thickness as comparedwith the length and width and a maximum thickness is restrictedarbitrarily, usually provided in the form of a roll (JIS K 6900).Therefore, among sheets, those having particularly small thicknesses maybe called films. However, there is no clear-cut boundary between “sheet”and “film” and these two are difficult to clearly distinguish one fromanother. Accordingly, as used herein, “sheet” may include “film” and“film” may include “sheet”.

The biodegradable sheet of the present invention is excellent in moldingprocessability and can be molded at a temperature at which no heating ofmolds is necessary and in a short molding cycle. Hereinafter, themolding method of the present invention will be described.

The biodegradable sheet of the present invention can be molded into amolded article by using a molding method such as vacuum forming, airpressure forming, vacuum-air pressure forming, press forming and so on.In this case, it is preferable that molding be performed at a sheettemperature not lower than the melting point of the polyester thatconstitutes the biodegradable sheet (Tm1) and lower than a temperatureby 30° C. higher than the melting point of the polyester (Tm1+30° C.).If the molding temperature is lower than the melting point of thepolyester (Tm1), heat resistance and molding processability may beunsatisfactory. If the molding temperature is not lower than (Tm1+30°C.), there will arise the problem of draw down of the sheet uponmolding.

In the present invention, it is preferable that the obtained moldedarticle be subjected to post-crystallization treatment. The method ofpost-crystallization is performed at a temperature not lower than theglass transition temperature of the polylactic acid resin thatconstitutes the sheet used and lower than the melting point of thepolyester that constitutes the sheet used. Post-crystallization maysometimes increase heat resistance. The heat resistance of the moldedarticle before the post-crystallization treatment depends on the meltingpoint of the polyester while the heat resistance of the molded articleafter the post-crystallization treatment depends on the melting point ofthe polylactic acid resin. For example, when a polyester having amelting point of 110° C. is used, the heat resistance temperature of themolded article before the post-crystallization treatment is 110° C. orless while the heat resistance temperature of the molded article afterthe post-crystallization treatment is elevated near the melting point ofthe polylactic acid resin. Note that although the melting point of thepolylactic acid resin may vary depending on the mixing ratios ofL-lactic acid and D-lactic acid as structural units, generally it isabout 135° C. to about 175° C. If the temperature ofpost-crystallization is lower than the glass transition temperature ofthe polylactic acid resin, crystallization of the polylactic acid resindoes not proceed substantially. On the other hand, if the temperature ofpost-crystallization is not lower than the melting point of thepolyester, the molded article will be deformed and there arises theproblem of precision of dimension. The time required forpost-crystallization is not particularly limited and preferably selecteddepending on the blending proportions as appropriate.

As described above, use of the biodegradable sheet of the presentinvention enables molded articles to be formed without retaining themold at a temperature near the crystallization of polylactic acid resin(for example, 80° C. to 130° C.), that is, at a molding temperaturelower than such a temperature and in a short molding cycle. Further, theobtained molded article has excellent heat resistance and excellentimpact resistance.

Molded articles of various forms can be formed by using thebiodegradable sheet of the present invention. Examples of molded articleinclude lunch boxes, trays or cups for foods such as fresh fish, meat,vegetables, soybean cake, daily dishes, desserts, and convenience foodnoodles, wrapping containers for tooth brushes, batteries, drugs,cosmetics and so on, hotfill containers for pudding, jam, curry and soon, or trays, carrier tapes and the like for transporting electroniccomponents such as IC, transistors, diodes and so on.

EXAMPLES

Hereinafter, the present invention will be described in detail byexamples. However, the present invention should not be considered to belimited to the examples. Measured values and evaluation methods used inthe examples and comparative examples are shown below.

(1) Evaluation of Heat Resistance

Molded articles obtained from biodegradable sheets were subjected toheat treatment at 80° C. or 120° C. for 20 minutes using an oven withinternal air circulation (“FC-610”, manufactured by Advantec), and thenleft to stand to cool to room temperature (23° C.±2° C.). Water at thesame temperature as the room temperature was poured into the moldedarticles after the heat treatment. The amount of water that filled themolded article after the heat treatment was defined as the volume of themolded article after the heat treatment. Separately, water at the sametemperature as the room temperature was poured into a molded articlethat was left to stand at the room temperature without subjecting toheat treatment in the same manner as described above. The amount ofwater that filled the molded article was defined as the volume of themolded article before the heat treatment. Then, a volume reduction ratio(%) of the molded article was calculated according to the followingequation. Note that a volume reduction ratio of below 3% means“excellent”, 6% or less means “practically usable range”, and above 6%means “unusable”.Volume reduction ratio={1−(volume of molded article after heattreatment/volume of molded article before heat treatment)}×100(2) Evaluation of Impact Resistance (1)

Using Hydrostat Impact Tester (Model HTM-1) manufactured by Toyo SeikiCo., Ltd., a percussion hammer having a diameter of 1/2 inch was hit ona biodegradable sheet at a speed of 3 m/sec at a temperature of 23° C.and energy required for breakage of the sheet was calculated.

(3) Evaluation of Impact Resistance (2)

Water was filled into a molded article obtained from a biodegradablesheet through an opening and the opening was sealed. The article wasmade to fall from a height of 1 m onto a concrete and whether or notdamage occurred was examined.

(4) Glass Transition Temperature

Glass transition temperature of a polyester was measured according toJapan Industrial Standard JIS-K-7121 by using a differential scanningcalorimeter (DSC) at a temperature elevation rate of 10° C./minute.

(5) Measurement of Degree of Crystallization

Heat of melting of crystal (ΔHm) and heat of crystallization (ΔHc)ascribable to the polylactic acid resin in the biodegradable sheet or inthe molded article were measured according to Japan Industrial StandardJIS-K-7121 by using a differential scanning calorimeter (DSC) at atemperature elevation rate of 10° C./min. and the degree ofcrystallization (%) of the polylactic acid resin was calculatedaccording to the following equation.Degree of crystallization={(ΔHm−ΔHc)/[92.8×(proportion of polylacticacid resin in sheet)]}×100(6) Evaluation of Moldability (1)

Using a mold having a diameter of 75 mm, a depth of 100 mm and a drawratio of 1.33 (mold temperature 25° C.), vacuum forming (degree ofvacuum: −70 cmHg) and mold forming condition of the molded article wasobserved. Evaluation was performed in four ranks. Evaluation standardsare as follows. “©” indicates the case where a molded article having anexcellent shape was formed, “◯” indicates the case where a moldedarticle having a good shape was formed, “Δ” indicates the case where amolded article that was substantially on a practically usable level, and“X” indicates the case where a molded article of unacceptable shape wasformed.

(7) Evaluation of Moldability (2)

Using a mold having a diameter of 75 mm, a depth of 37.5 mm and a drawratio of 0.5 (mold temperature 25° C.), vacuum forming (degree ofvacuum: −70 cmHg) and mold forming condition of the molded article wasobserved. Evaluation was performed in four ranks. Evaluation standardsare as follows. “⊚” indicates the case where a molded article having anexcellent shape was formed, “◯” indicates the case where a moldedarticle having a good shape was formed, “Δ” indicates the case where amolded article that was substantially on a practically usable level, and“X” indicates the case where a molded article of unacceptable shape wasformed.

Example 1

15 ppm of tin octylate was added to 100 kg of L-Lactide (tradename:PURASORB L) manufactured by Purac Japan Co. and the resultant wascharged in a 500-L batch type polymerization tank equipped with astirrer and a heater. The tank was purged with nitrogen andpolymerization was performed at 185° C. for 60 minutes at an agitationspeed of 100 rpm. The obtained melt was fed to a 40 mmφ unidirectionalbiaxial extruder equipped with 3 stages of vacuum vent manufactured byMitsubishi Heavy Industries, Ltd., and extruded at 200° C. into a strandand pelletized while removing volatiles at a vent pressure of 4 Torr.The obtained polylactic acid resin had a weight average molecular weightof 200,000 and a L-form content of 99.5%. The resin had a melting pointby DSC of 171° C. and a glass transition temperature of 58° C.

The obtained polylactic acid resin and a polybutyrene succinate(“Bionolle 1903”, trade name, manufactured by Showa Highpolymer Co.,Ltd., melting point: 110° C., glass transition temperature: −40° C.) asa biodegradable aliphatic polyester, were mixed in proportions ofpolylactic acid resin/biodegradable aliphatic polyester=70 mass %/30mass %. The resultant was fed to a unidirectional biaxial extruder,melt-kneaded and extruded into a strand, and then cut by a pelletizer toobtain pellets. Subsequently, the obtained pellets were dried at 70° C.for 8 hours, fed to a monoaxial extruder, and extruded through a T-dieto obtain a 400 μm-thick biodegradable sheet. The polylactic acid resinof the obtained biodegradable sheet had a degree of crystallization of11%.

Then, a molded article was formed using the obtained biodegradablesheet. That is, using a mold having a diameter of 75 mm and a depth of100 mm (a draw ratio of 1.33) (mold temperature 25° C.), vacuum formingwas performed under the conditions of a sheet temperature of 120° C.shown in table 1 and a vacuum pressure of −70 cmHg to obtain abiodegradable molded article. The obtained molded article was evaluatedfor heat resistance at 80° C. for 20 minutes, impact resistance (1),impact resistance (2), and moldability (1). The results obtained areshown in Table 1.

Example 2

A biodegradable sheet was obtained in the same manner as that in Example1 except that the blending amounts of polylactic acid resin andbiodegradable aliphatic polyester were changed to polylactic acidresin/biodegradable aliphatic polyester=60 mass %/40 mass %. Thepolylactic acid resin of the obtained biodegradable sheet had a degreeof crystallization of 10%.

Further, using the obtained biodegradable sheet, a molded article wasobtained in the same manner as that in Example 1. The obtained moldedarticle was evaluated in the same manner as that in Example 1. Theresults obtained are shown in Table 1.

Example 3

A biodegradable sheet was obtained in the same manner as that in Example1 except that the blending amounts of polylactic acid resin andbiodegradable aliphatic polyester were changed to polylactic acidresin/biodegradable aliphatic polyester=50 mass %/50 mass %. Thepolylactic acid resin of the obtained biodegradable sheet had a degreeof crystallization of 8%.

Further, using the obtained biodegradable sheet, a molded article wasobtained in the same manner as that in Example 1. The obtained moldedarticle was evaluated in the same manner as that in Example 1. Theresults obtained are shown in Table 1.

Example 4

A biodegradable sheet was obtained in the same manner as that in Example1 except that the blending amounts of polylactic acid resin andbiodegradable aliphatic polyester were changed to polylactic acidresin/biodegradable aliphatic polyester=40 mass %/60 mass %. Thepolylactic acid resin of the obtained biodegradable sheet had a degreeof crystallization of 10%.

Further, using the obtained biodegradable sheet, a molded article wasobtained in the same manner as that in Example 1. The obtained moldedarticle was evaluated in the same manner as that in Example 1. Theresults obtained are shown in Table 1.

Example 5

A biodegradable sheet was obtained in the same manner as that in Example1 except that polybutyrene adipate terephthalate (“Ecoflex” manufacturedby BASF, melting point: 109° C., glass transition temperature: −30° C.)was used as a biodegradable aliphatic polyester and the blending amountsof polylactic acid resin and biodegradable aliphatic polyester werechanged to polylactic acid resin/biodegradable aliphatic polyester=70mass %/30 mass %. The polylactic acid resin of the obtainedbiodegradable sheet had a degree of crystallization of 8%.

Further, using the obtained biodegradable sheet, a molded article wasobtained in the same manner as that in Example 1. The obtained moldedarticle was evaluated in the same manner as that in Example 1. Theresults obtained are shown in Table 1.

Example 6

15 ppm of tin octylate was added to 90 kg of L-Lactide (trade name:PURASORB L) manufactured by Purac Japan Co. and 10 kg of DL-lactide(trade name: PURASORB DL) manufactured by the same company, and theresultant was charged in a 500-L batch type polymerization tank equippedwith a stirrer and a heater. The tank was purged with nitrogen andpolymerization was performed at 185° C. for 60 minutes at an agitationspeed of 100 rpm. The obtained melt was fed to a 40 mmφ unidirectionalbiaxial extruder equipped with 3 stages of vacuum vent manufactured byMitsubishi Heavy Industries, Ltd., and extruded at 200° C. into a strandand pelletized while removing volatiles at a vent pressure of 4 Torr.The obtained polylactic acid resin had a weight average molecular weightof 200,000 and a L-form content of 94.8%. The resin had a melting pointby DSC of 165° C. and a glass transition temperature of 56° C.

The obtained polylactic acid resin and a polybutyrene succinate(“Bionolle 1903”, trade name, manufactured by Showa Highpolymer Co.,Ltd., melting point: 110° C., glass transition temperature: −40° C.) asa biodegragable aliphatic polyester, were mixed in proportions ofpolylactic acid resin/biodegradable aliphatic polyester=60 mass %/40mass %. The resultant was fed to a unidirectional biaxial extruder,melt-kneaded and extruded into a strand, and then cut by a pelletizer toobtain pellets. Subsequently, the obtained pellets were dried at 70° C.for 8 hours, fed to a monoaxial extruder, and extruded through a T-dieto obtain a 400 μm-thick biodegradable sheet. The polylactic acid resinof the obtained biodegradable sheet had a degree of crystallization of4%.

Then, using the obtained biodegradable sheet, a molded article wasobtained in the same manner as that in Example 1. The obtained moldedarticle was evaluated in the same manner as that in Example 1. Theresults obtained are shown in Table 1.

Example 7

The molded article obtained in Example 2 was subjected topost-crystallization treatment at 70° C. for 8 hours to obtain apost-crystallized molded article. The polylactic acid resin of theobtained molded article had a degree of crystallization of 45%. Theobtained molded article was evaluated for heat resistance at 120° C. for20 minutes, impact resistance (1), impact resistance (2), andmoldability (1). The results obtained are shown in Table 1.

Example 8

The polylactic acid resin obtained in Example 1 and a polybutyrenesuccinate (“Bionolle 1903”, trade name, manufactured by ShowaHighpolymer Co., Ltd., melting point: 110° C., glass transitiontemperature: −40° C.) as a biodegragable aliphatic polyester, were mixedin proportions of polylactic acid resin/biodegradable aliphaticpolyester=70 mass %/30 mass %. The resultant was fed to a unidirectionalbiaxial extruder, melt-kneaded and extruded into a strand, and then cutby a pelletizer to obtain pellets. Subsequently, the obtained pelletswere dried at 70° C. for 8 hours, fed to a monoaxial extruder, extrudedthrough a T-die, and then made contact a cast roll at 110° C. to obtaina 400 μm-thick biodegradable sheet. The polylactic acid resin of theobtained biodegradable sheet had a degree of crystallization of 43%.

Then, using the obtained biodegradable sheet, a molded article wasobtained in the same manner as that in Example 1. The obtained moldedarticle was evaluated in the same manner as that in Example 1. Theresults obtained are shown in Table 1. TABLE 1 Example Example ExampleExample Example Example Example Example 1 2 3 4 5 6 7 8 Blending A*¹ 7060 50 40 70 60 60 70 ratio (mass %) B*² 30 40 50 60 30 40 40 30 Degreeof Sheet 11 10 8 10 8 4 10 43 Crystallization (%) Molded — — — — — — 45— article Molding temperature (° C.)*³ 120 120 120 120 120 120 120 120Heat Volume reduction 1.1 1.0 0.9 0.9 1.3 1.2 0.1 0.3 resistance ratio(%) Impact resistance (1) 108 150 230 301 140 162 146 100 (Kgf · mm)Impact resistance (2) No No No No No No No No breakage breakage breakagebreakage breakage breakage breakage breakage Evaluation of moldability ◯◯ ◯ ◯ ◯ ◯ ◯ Δ Post-crystallization No No No No No No Yes NoNotes)*¹Polylactic acid resin: Glass transition temperature 58° C., meltingpoint 171° C.; However polylactic acid resin of Example 6: Glasstransition temperature 56° C., melting point 165° C.;*²Biodegradable aliphatic polyester: “Bionolle 1903” (glass transitiontemperature −40° C., melting point 110° C.), or “Ecoflex” (glasstransition temperature −30° C., melting point 109° C.);*³Molding temperature: Temperature of biodegradable sheet upon molding.

Example 9

The 400-μm thick biodegradable sheet obtained in Example 1 and the400-μm thick biodegradable sheet obtained in Example 8 were alsoevaluated for moldability (2). That is, each sheet was subjected tovacuum forming (degree of vacuum: −70 cmHg) using a mold having adiameter of 75 mm, a depth of 37.5 mm and a draw ratio of 0.5 (moldtemperature 25° C.). The obtained molded articles were evaluated formoldability (2). The results obtained are shown in Table 2. TABLE 2Example 1 Example 8 Blending proportion A*⁴ 70 70 (mass %) B*⁵ 30 30Degree of crystallization Sheet 11 43 (%) Molding temperature (° C.)*³120 120 Evaluation of moldability ⊚ ◯ Post-crystallization No NoNotes*³Molding temperature: Temperature of biodegradable sheet upon molding;*⁴Polylactic acid resin: Glass transition temperature 58° C., meltingpoint 171° C.;*⁵Biodegradable aliphatic polyester: “Bionolle 1903” (glass transitiontemperature −40° C., melting point 110° C.)

Comparative Example 1

The polylactic acid resin obtained in Example 1 was fed to aunidirectional biaxial extruder, melt-kneaded and extruded into astrand, and then cut by a pelletizer to obtain pellets. Subsequently,the obtained pellets were dried at 70° C. for 8 hours, fed to amonoaxial extruder, and extruded through a T-die to obtain a 400μm-thick biodegradable sheet. The polylactic acid resin of the obtainedbiodegradable sheet had a degree of crystallization of 6%.

Then, a molded article was formed using the obtained biodegradablesheet. That is, using a mold having a diameter of 75 mm and a depth of100 mm (a draw ratio of 1.33) (mold temperature 25° C.), vacuum formingwas performed under the conditions of a sheet temperature of 80° C.shown in Table 2 and a vacuum pressure of −70 cmHg to obtain abiodegradable molded article. The obtained molded article was evaluatedin the same manner as that in Example 1. The results obtained are shownin Table 2.

Comparative Example 2

A biodegradable sheet was obtained in the same manner as that in Example1 except that the blending amounts of polylactic acid resin andbiodegradable aliphatic polyester were changed to polylactic acidresin/biodegradable aliphatic polyester=80 mass %/20 mass %. Thepolylactic acid resin of the obtained biodegradable sheet had a degreeof crystallization of 8%.

Further, using the obtained biodegradable sheet, a molded article wasobtained in the same manner as that in Example l. The obtained moldedarticle was evaluated in the same manner as that in Example 1. Theresults obtained are shown in Table 3. TABLE 3 Comparative ComparativeExample 1 Example 2 Blending proportion A*⁴ 100 80 (mass %) B*⁵ 0 20Degree of Sheet 6 8 crystallization (%) Molded — — article Moldingtemperature *³ 80 120 Heat Volume reduction 99.8 10.1 resistance ratio(%) Impact resistance (1) (Kgf · mm) 12 150 Impact resistance (2) CracksNo breakage Evaluation of moldability ◯ ◯ Post-crystallization No NoNotes*³Molding temperature: Temperature of biodegradable sheet upon molding;*⁴Polylactic acid resin: Glass transition temperature 58° C., meltingpoint 171° C.;*⁵Biodegradable aliphatic polyester: “Bionolle 1903” (glass transitiontemperature −40° C., melting point 110° C.)

Tables 1 and 3 indicate that Examples 1 to 7 were excellent in all ofthe heat resistance, impact resistance, and moldability and that goodmolded articles can be obtained by an ordinary molding cycle. Inparticular, Example 7 showed that the heat resistance was increased dueto the effect of post-crystallization, and the heat resistancetemperature was higher than the melting point or more of thebiodegradable aliphatic polyester. Further, Example 8 were excellent inthe heat resistance and impact resistance, and showed moldability on apractically usable level. Note that the sheets obtained in Examples 1 to8 were biodegradable so that they would cause no environmental problems.

On the other hand, in Comparative Example 1, problems arose in the heatresistance and impact resistance since no biodegradable aliphaticpolyester was contained. In Comparative Example 2, the heat resistancewas poor due to a decreased blending amount of the biodegradablealiphatic polyester.

Table 2 indicates that when the draw ratio was 0.5, the sheet of Example1 showed excellent moldability and the sheet of Example 8 showed goodmoldability. That is, the biodegradable sheets of Examples 1 to 8 of thepresent invention gave good molded articles so far as the draw ratio was0.5, and even when the draw ratio was 1.33, molded articles on apractically usable level could be obtained. Of course, excellent moldedarticles could be obtained when the draw ratio was less than 0.5.

As described in detail, according to the present invention,biodegradable sheets that are biodegradable and exhibit excellent heatresistance, excellent impact resistance and excellent moldability can beprovided. Further, When molded articles are formed by using thebiodegradable sheets of the present invention, the temperature of moldneed not be retained at a temperature near crystallization temperatureof polylactic acid resin (80° C. to 130° C.), and molded articles havingheat resistance can be obtained by using molds at room temperature,which makes it possible to perform molding in an ordinary molding cycle.That is, by blending a polylactic acid resin and a specified polyesterin predetermined proportions and controlling the degree ofcrystallization of the polylactic acid resin in the resultant sheet, theproblems of the conventional technology, that is, (1) prolonged moldingcycle and increased production costs, (2) necessity of installment orthe like for heating molds, and so on have been solved. Further, use ofthe biodegradable sheets of the present invention enables one to performvarious forming such as vacuum forming, air pressure forming, vacuum-airpressure forming, and press forming. In particular, even when deep-drawnmolded articles and blister molded articles having a complicated shapeare formed by using a vacuum forming machine, good molded articles canbe obtained. Furthermore, by performing molding under specifiedconditions, molded articles having excellent heat resistance, excellentimpact resistance, and excellent moldability can be provided andpost-crystallization of the molded articles under specified conditionscan provide molded articles having further increased heat resistance.

INDUSTRIAL APPLICABILITY

The present invention is applicable to food containers, cups and traysfor foods, wrapping containers, hot-fill containers, trays and carriertapes for transporting electronic parts, and so on.

1. A biodegradable sheet comprising a resin composition, wherein theresin composition containing 75 to 25 mass % of a polylactic acid resinand 25 to 75 mass % of a polyester having a glass transition temperatureof 0° C. or less and a melting point higher than the glass transitiontemperature of the polylactic acid resin based on total 100 mass %,wherein the polylactic acid resin in the sheet has a degree ofcrystallization of 45% or less.
 2. A biodegradable sheet comprising aresin composition, wherein the resin composition containing 75 to 25mass % of a polylactic acid resin and 25 to 75 mass % of a polyesterhaving a glass transition temperature of 0° C. or less and a meltingpoint of 90° C. or more, and wherein the polylactic acid resin in thesheet has a degree of crystallization of 45% or less.
 3. Thebiodegradable sheet according to claim [[1 or]] 2, wherein thepolylactic acid resin has a degree of crystallization of 20% or less. 4.The biodegradable sheet according to claim 3, wherein the polyester is abiodegradable aliphatic polyester other than the polylactic acid resin.5. A biodegradable sheet comprising a resin composition, wherein theresin composition containing 75 to 25 mass % of a polylactic acid resinand 25 to 75 mass % of a polyester having a glass transition temperatureof 0° C. or less and a melting point higher than the glass transitiontemperature of the polylactic acid resin based on total 100 mass %, andwherein a molded article molded from the sheet has a volume reductionratio of 6% or less.
 6. A biodegradable sheet for deep-drawing,comprising a resin composition, wherein the resin composition containing75 to 25 mass % of a polylactic acid resin and 25 to 75 mass % of apolyester having a glass transition temperature of 0° C. or less and amelting point higher than the glass transition temperature of thepolylactic acid resin based on total 100 mass %, and wherein thepolylactic acid resin in the sheet has a degree of crystallization of45% or less.
 7. A molded article molded from a sheet that comprises aresin composition, wherein the resin composition containing 75 to 25mass % of a polylactic acid resin and 25 to 75 mass % of a polyesterhaving a glass transition temperature of 0° C. or less and a meltingpoint higher than the glass transition temperature of the polylacticacid resin based on total 100 mass %, and having a volume reductionratio of 6% or less.
 8. A molded article molded from a biodegradablesheet that comprises a resin composition, wherein the resin compositioncontaining 75 to 25 mass % of a polylactic acid resin and 25 to 75 mass% of a polyester having a glass transition temperature of 0° C. or lessand a melting point higher than the glass transition temperature of thepolylactic acid resin based on total 100 mass %, and wherein thepolylactic acid resin in the sheet has a degree of crystallization of45% or less, at a temperature not lower than a melting point of thepolyester and lower than a temperature by 30° C. higher than the meltingpoint of the polyester, and having a volume reduction ratio of 6% orless.
 9. The molded article according to claim 8, which is molded from abiodegradable sheet that comprises a resin composition, wherein theresin composition containing 75 to 25 mass % of a polylactic acid resinand 25 to 75 mass % of a polyester having a glass transition temperatureof 0° C. or less and a melting point higher than the glass transitiontemperature of the polylactic acid resin based on total 100 mass %, andwherein the polylactic acid resin in the sheet has a degree ofcrystallization of 45% or less, at a temperature not lower than amelting point of the polyester and lower than a temperature by 30° C.higher than the melting point of the polyester, and thenpost-crystallized at a temperature not lower than the glass transitiontemperature of the polylactic acid resin and lower than the meltingpoint of the polyester, and having a volume reduction ratio of 6% orless.
 10. A method for producing a molded article, comprising forming amolded article from a biodegradable sheet that comprises a resincomposition, wherein the resin composition containing 75 to 25 mass % ofa polylactic acid resin and 25 to 75 mass % of a polyester having aglass transition temperature of 0° C. or less and a melting point higherthan the glass transition temperature of the polylactic acid resin basedon total 100 mass %, and wherein the polylactic acid resin in the sheethas a degree of crystallization of 45% or less, at a temperature notlower than a melting point of the polyester and lower than a temperatureby 30° C. higher than the melting point of the polyester.
 11. The methodfor producing a molded article according to claim 10, further comprisingpost-crystallizing the molded article formed from the biodegradablesheet at the molding temperature, at a temperature not lower than theglass transition temperature of the polylactic acid resin and lower thanthe melting point of the polyester.
 12. The biodegradable sheetaccording to claim 1, wherein the polylactic acid resin has a degree ofcrystallization of 20% or less.
 13. The biodegradable sheet according toclaim 12, wherein the polyester is a biodegradable aliphatic polyesterother than the polylactic acid resin.
 14. The biodegradable sheetaccording to claim 1, wherein the polyester is a biodegradable aliphaticpolyester other than the polylactic acid resin.
 15. The biodegradablesheet according to claim 2, wherein the polyester is a biodegradablealiphatic polyester other than the polylactic acid resin.